Python C Module example: building a simplistic hash table with the help of some Redis libraries (https://github.com/antirez/redis - http://redis.io/).

python-c-module-example.c

/*
  - setup.py
      from distutils.core import setup, Extension
      module = Extension('ht', sources = ['zmalloc.c', 'sds.c', 'dict.c', 'python-c-module-example.c'])
      setup(name = 'Hash Table', version = '1.0', ext_modules = [module])
      
  - install.sh
      # Fetch dependencies from https://github.com/antirez/redis 
      wget https://raw.github.com/antirez/redis/2.6/src/fmacros.h
      wget https://raw.github.com/antirez/redis/2.6/src/config.h
      wget https://raw.github.com/antirez/redis/2.6/src/dict.h
      wget https://raw.github.com/antirez/redis/2.6/src/dict.c
      wget https://raw.github.com/antirez/redis/2.6/src/zmalloc.h
      wget https://raw.github.com/antirez/redis/2.6/src/zmalloc.c
      wget https://raw.github.com/antirez/redis/2.6/src/sds.h
      wget https://raw.github.com/antirez/redis/2.6/src/sds.c
      cp /usr/include/assert.h redisassert.h
      # Compile the extension
      python setup.py install && python ./test.py
      rm fmacros.h config.h dict.* zmalloc.* sds.* redisassert.h
      
  - test.py
      import ht
      ht.set('key:1', 'aaaa')
      ht.set('key:2', 'bbbb')
      print ht.get('key:1')
      print ht.exists('key:1')
      print ht.exists('a random key')
      print ht.delete('key:1')
      print ht.get('key:1')
*/

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <stdarg.h>
#include <limits.h>
#include <sys/time.h>
#include <ctype.h>
#include <Python.h>
#include "sds.h"

typedef unsigned short int bool;
#define true 1
#define false 0
#define BUCKETS 128

typedef struct Entry {
  unsigned int hash;
  sds key;
  sds value;
} Entry;

typedef struct Bucket {
  unsigned long size;
  Entry *table;
} Bucket;

typedef struct HTable {
  unsigned long length;
  Bucket buckets[BUCKETS];
} HTable;

/* 
  This is a global object which may not be the best solution, 
  but will do for the example 
*/
static HTable HT;

static PyObject *ht_set(PyObject *self, PyObject *args) {
  char *value, *key;
  if ( !PyArg_ParseTuple(args, "ss", &key, &value) )
    return NULL;
  char *k = sdsnew(key);
  char *v = sdsnew(value);
  unsigned int hash = dictGenHashFunction(k, sdslen(k));
  unsigned short int bucket = hash % BUCKETS;  
  unsigned long position = HT.buckets[bucket].size;
  if ( position == 0 ){
    HT.buckets[bucket].table = (Entry*)malloc(sizeof(Entry));
  } else {
    HT.buckets[bucket].table = (Entry*)realloc(HT.buckets[bucket].table, sizeof(Entry)*(position + 1));
  }
  HT.buckets[bucket].table[position].hash = hash;
  HT.buckets[bucket].table[position].key = k;
  HT.buckets[bucket].table[position].value = v;
  HT.buckets[bucket].size += 1;
  HT.length += 1;
  return Py_BuildValue("iiss", bucket, hash, HT.buckets[bucket].table[position].key, HT.buckets[bucket].table[position].value);
}

static PyObject *ht_length(PyObject *self, PyObject *args) {
  return Py_BuildValue("i", HT.length);
}

Entry * find(char *key) {
  char *k = sdsnew(key);
  unsigned int hash = dictGenHashFunction(k, sdslen(k));
  unsigned short int bucket = hash % BUCKETS;
  Bucket object_bucket = HT.buckets[bucket];
  Entry *e;
  unsigned long c = 0;
  bool found = false;
  /* This is a list lookup for the time ... */
  for(c=0; c < object_bucket.size; c++){
    if ( object_bucket.table[c].hash == hash ){
      e = &object_bucket.table[c];
      found = true;
      break;
    }
  }
  if ( found ){
    return e;
  } else { 
    return NULL;
  }
}

static PyObject *ht_exists(PyObject *self, PyObject *args) {
  char *key;
  if ( !PyArg_ParseTuple(args, "s", &key) )
    return NULL;
  if ( find(sdsnew(key)) ) {
    Py_RETURN_TRUE;
  } else {
    Py_RETURN_FALSE;
  }
}

static PyObject *ht_del(PyObject *self, PyObject *args) {
  char *key;
  if ( !PyArg_ParseTuple(args, "s", &key) )
    return NULL;
  Entry *e = find(sdsnew(key));
  if ( e ) {
    unsigned int hash = (*e).hash;
    char *value = (*e).value;
    // instead of deleting we nullify the record in-place
    (*e).hash = 0;
    (*e).key = sdsnew("");
    (*e).value = sdsnew("");
    return Py_BuildValue("iss", hash, key, value);
  } else {
    Py_RETURN_NONE;
  } 
}

static PyObject *ht_get(PyObject *self, PyObject *args) {
  char *key;
  if ( !PyArg_ParseTuple(args, "s", &key) )
    return NULL;
  Entry *e = find(sdsnew(key));
  if ( e ) {
    return Py_BuildValue("iss", (*e).hash, (*e).key, (*e).value);
  } else {
    Py_RETURN_NONE;
  }
}

static PyMethodDef HtMethods[] = {
  {"set",    ht_set,    METH_VARARGS, "Add a key-value to the table"},
  {"get",    ht_get,    METH_VARARGS, "Get a value from the table"},
  {"delete", ht_del,    METH_VARARGS, "Delete a key-value from the table"},
  {"exists", ht_exists, METH_VARARGS, "Check if a key exists in the table"},
  {"length", ht_length, METH_VARARGS, "Get the current table size"},
  {NULL, NULL, 0, NULL}
};

void initht(void) {
  (void) Py_InitModule("ht", HtMethods);
}